I disagree - Outlook is a walled garden of closed standards, and it makes users vulnerable to the whims of Microsoft or dependent entirely on their office ecosystem.
The recent outlook hack with senior accounts hacked and only being informed by Microsoft of the hack 1 year later is a good example.
Outlook is superficially good but essentially big businesses and organisations are locked in to a proprietary system for email and calendars and entirely reliant on Microsoft to keep their data secure.
I’m actually surprised Antitrust laws aren’t used to break up the Office 365 monopoly. Only the teams integration is being challenged but the tight integration between Outlook, Office and OneDrive is monopolistic. Other services could integrate in the same way if Microsoft was forced to open up its APIs, which would be good for competition and customers.
At the moment you pretty much have to go all in with Office or forgo major integration benefits if you want to use different cloud or mail services. Why do you need 1 single provider for office software, mail and cloud storage?
Atomic systems or rpm-ostree is an interesting concept and may well be the future of distributing linux, but it has a lot of compromises. It may not be the first place to start when leaving windows.
The problem is all the apps and things you may wish to do with your OS. Flatpak is the preferred method of installing apps as it doesn’t interfere with the OS, but that is a compromise that means more overhead for running apps including memory and disk space, and less integration with the host OS than traditional apps.
You can overlay native apps but the more you overlay onto the immutable os, the more complex upgrading gets and the risks of breaking stuff.
I’m not sure I would be starting with an immutable OS when switching away from windows. While it has a lot of theoretical benefits, its a work in progress and with significant compromises at the moment. Your VPN may just be the first of many programmes you find you need to overlay.
I personally would look at a more traditional install, get it working how you like and if you find Linux works as a permanent home then think about how you might recreate that with an immutable OS base. If your needs a re very simple then maybe it’ll be easy, but if you’re using lots of software and tools (particularly if its not available Flatpak) or custom OS config you may find atomic desktops are not yet quite ready for you.
It could be frustrating and off putting if you try linux immutable, find loads of problems and attribute that to linux when its actually the immutable OS that’s the cause.